The Best Battery Cases for iPhone 6, 6s, 6 Plus, and 6s Plus

Updated September 8, 2016

iPhone 6/6s and 6 Plus/6s Plus cases do not fit the new iPhone 7 and 7 Plus, respectively. On the new phones, the camera is repositioned, and the ports array along the bottom is slightly different. We’ll…

iPhone 6/6s and 6 Plus/6s Plus cases do not fit the new iPhone 7 and 7 Plus, respectively. On the new phones, the camera is repositioned, and the ports array along the bottom is slightly different. We’ll be researching and testing iPhone 7/7 Plus cases for a full guide. Don’t buy an older case expecting it to fit either new handset.

Your guide

Nick Guy

While the initial batch of iPhone 6 battery cases was pretty small, the number of available models has grown significantly. We’ve now tested 28 different battery cases (24 for the iPhone 6 and 6s and four for the iPhone 6 and 6s Plus) over the course of more than 220 hours. The best iPhone 6/6s battery case for most people is Anker’s Ultra Slim Extended Battery Case. It provides up to 117 percent of a full charge to the iPhone 6—one full charge plus another 17 percent—and at only $40, it’s by far the most affordable. Its low price and fairly high capacity mean that it offers the highest ratio of charge percent per dollar, and the lowest cost for a full charge of your phone. It’s also one of the lightest and thinnest cases we tested. The results with the iPhone 6s were slightly lower in our testing, but the Anker still bested the competition.

Buying Options

The Anker’s matte-plastic case isn’t the most protective of the battery cases we tested, but it offers a perfectly acceptable level of coverage, and it feels like it should last the life of the iPhone it covers. And installation is about as easy as it gets: Remove a cap at the top of the case, slide the phone in, and then simply replace the cap—we prefer this approach to the snap-on frame found on some competitor's cases, including the otherwise-excellent Incipio offGRID Express. A single button on the Anker both toggles the battery’s charging circuitry and lights up a row of four LEDs that show the remaining battery life. All in all, it’s not the prettiest case, but it gets the job done. It’s a bit more user-friendly and familiar-feeling than other, more novel designs such as the Tylt Energi, and it’s considerably less expensive than anything else.

Buying Options

If the highest possible capacity at a reasonable price is your most important consideration, Anker’s Premium Extended Battery Case is the way to go. It costs $20 more than our top pick, and it’s slightly larger and heavier, but it provides 142 percent of a full iPhone 6 charge (one of the highest figures we saw from any case) at a price that’s less than that of most of the “standard capacity” models from other companies. While it seems to be based on a common OEM design, the numbers speak for themselves: This one comes in just below the Ultra Slim Battery Case in terms of charge percent per dollar, and it’s the most efficient battery when viewed in terms of percent charge per mAh.

Buying Options

Prong’s PWR Case is a more advanced (and more expensive option). It separates the case from the battery, so you don’t need to keep the battery pack attached unless you’re actively charging your phone—a big advantage for anyone with tight pockets. The 2600-mAh battery sled also has built-in wall-outlet prongs that fold out when you need to charge the case’s battery, eliminating the need to carry a separate cable or charger. The downside is that the case and battery together are bigger than any of the other battery cases we tested. But for some people, it’ll be a convenient design that’s worth a higher price.

Buying Options

We were surprised when Apple quietly launched its Smart Battery Case at the end of 2015. It’s the first case of its kind from Apple, and to some, it’s a tacit acknowledgment that battery life of the the iPhone 6 and 6s could be more impressive. Most first impressions–ours included!–noted that Apple’s entry in this field looks weird thanks to a protruding bump on the back, and its 1,877-mAh capacity is quite low for the price, given the competition. However, it looks—and feels—a lot better in person, and unique features such as Lightning-connector charging, an onscreen battery-level indicator, and a “passive coupled antenna” to keep the case from affecting cellular activity make it worth considering if you’re willing to spend the extra cash.

Buying Options

We have a pick for iPhone 6 Plus and 6s Plus users as well—or at least for the few who actually need more juice than the Plus models themselves provide: The larger version of Tylt’s $100 Energi Sliding Power Case is the best of the three iPhone 6 Plus/6s Plus models we tested. It has the highest-capacity battery, provides the greatest charge in the fastest amount of time, and offers the highest charge per dollar. It also has the same slide-out design as its smaller sibling. This means you don’t need to keep the larger battery pack on the phone at all times, a big advantage when it comes to the already large Plus-size iPhones.

We have tested the battery cases available for the iPhone 7 and 7 Plus, and discuss our favorites in our piece on cases for those phones. For those using an iPhone SE, 5, or 5s, we have a pick for the best battery case for that model as well. And if you’re using another device (or a different case) and still want some external battery juice, we cover four categories of external USB batteries in this guide.

Why you should trust me

I was the accessories editor at iLounge for a little more than three years. During my tenure, I reviewed more than 1,000 products, and almost 100 of those were battery cases. I’ve probably tested more iPhone battery cases than anyone on the planet, giving me a particularly experienced perspective and depth of knowledge when it comes to these accessories. Heck, I even keep a spreadsheet that calculates the results I expect to see from a battery based on the average results of similar battery cases that came before it.

Why you might want (or not want) a battery case

According to iFixit, the iPhone 6s has a 1715-mAh battery, and the iPhone 6 has 1810 mAh, compared to the 1560-mAh cell found in the iPhone 5s. The iPhone 6s and 6 also have much larger screens, which use more power, but Apple says you should expect the iPhone 6 to provide up to 14 hours of talk time (versus 10 with the 5s), 250 hours of standby time (the same as with the 5s), 10 hours of LTE browsing (the same), 11 hours of Wi-Fi browsing (versus 10), 11 hours of video playback (versus 10), or 50 hours of audio playback (versus 40)—with the caveat that all those estimates are prefaced by “up to.” Apple’s estimates for the iPhone 6s are identical to those for the 6.

iLounge is one of the few publications to run comparative battery tests. “In our most aggressive battery test, game playback, which typically runs an iPhone down around three times normal speed, we ran the graphically demanding Infinity Blade III at 50 percent brightness and 50 percent speaker volume until the battery drained,” editor-in-chief Phil Dzikiy wrote. “On the iPhone 6, the game ran for 3 hours and 57 minutes, up from 3 hours and 42 minutes on the iPhone 5s”—an increase of 12 percent.

The differences in battery life between an iPhone 6 or 6s and the iPhone 5s are admittedly small, but there is a good chance you’ll get longer battery life from an iPhone 6 or 6s than you would from your previous iPhone—especially if you’re upgrading from a years-old 5s, which most certainly has some amount of battery degradation.

That said, depending on how you’re using the handset, it’s still easy to drain your phone’s battery in an average day. Although we have some tips on extending smartphone battery life, anyone who has trouble getting their phone to last the day and doesn’t have the time (or physical access) to plug into a wall outlet might find that a battery case—which puts a moderate-capacity rechargeable battery inside a (bulky) iPhone case—is a smart choice. In the best circumstances, a battery case can double the battery life of your iPhone and then some. And unlike with stand-alone battery packs, there’s no need to tote a separate cable or to figure out how to carry both devices together. You just slide or snap the iPhone into the case, and you have protection and power in a single unit. Plus, we recommend using a case anyway.

Of course, some people prefer to use their iPhones au naturale—they just don’t want the extra bulk and weight a battery case adds. If so, plenty of other on-the-go charging options are available, most notably standalone battery packs. Portable battery packs can fit in your pocket and juice up an iPhone one or two times, while larger packs can keep you going for days at a time. We also discuss, below, phone-sized batteries that aren’t built into cases.

How we picked and tested

Unlike with many other categories of products we test—including battery cases for older iPhones—there isn’t a lot of competition to wade through to find the products that deserve testing. Thanks to Apple’s MFi certification process, no officially-certified iPhone 6 battery case made it to market before January 2015. While there are non-certified models to be found across the web, such as Amazon’s current top seller, we recommend avoiding them. Lacking MFi certification doesn’t necessarily mean a product is poor, but it does mean that there are no quality or compatibility guarantees, and there’s always the possibility that an iOS update will break compatibility. For these reasons, we limit our testing—and, thus, our recommendations—to MFi-certified battery cases.

To test each battery case, we installed a fully drained iPhone 6, set to Airplane mode, in the fully charged case.1 When the iPhone reached a 100 percent charge–or when it stopped charging–we removed it from the case. Assuming the battery case still had remaining charge, we drained the phone’s battery again and then installed the phone in the case a second time, noting the phone’s battery percentage when the case stopped charging it. We recorded the charge percentages and times for each test, as well as the physical dimensions and weight of each battery case. Each test was repeated a few days later and then once more for a total of three tests. We then averaged the charge results. The same tests were run with the iPhone 6 Plus and its cases, and repeated with the iPhone 6s and 6s Plus as necessary.

We also tested each case for subjective aspects of usability, such as how easy it is to press the buttons and how the encased phone feels in the hand. None of the packs we tested allow easy docking with Lightning-connector dock-cradle accessories, but none were particularly tough to install or remove. (Mophie has traditionally used a removable-bottom design, but the company’s upcoming iPhone 6 models are moving away from that approach.)

Additionally, we used a micro USB cable to connect each battery case to a computer to test whether or not each allows for pass-through charging (the capability to charge the iPhone while it’s in the case) and data syncing.

As a final note, it’s important to point out that the charging performance for each case depends on a number of factors. Specifically, the battery usage of the iPhone itself varies based on cellular signal strength, your use of location services, background processes, the apps you’re using, and more—and the more power your phone is using, the faster it’s using both its own battery and any attached battery case. In other words, your mileage will likely vary.

Buying Options

The iPhone 6/6s battery case with the best combination of good performance, price for the capacity, and size (the amount of bulk it adds to the phone) is Anker’s Ultra Slim Extended Battery Case. It has the capability to provide 117 percent of a full charge to an iPhone 6. The $40 price tag is crazy low for a battery case, and Anker has confirmed it’s a permanent price, not just a temporary promotion. We’ve never seen a battery case from a name-brand manufacturer so low, so early. At that price, it offers the best charge value (2.9 percent charge per dollar, or $34.34 for a full charge) of any of the cases we tested, by far. The numbers weren’t identical with the iPhone 6s, but they were still good enough that we’re confident keeping this as our pick for the 6s, as well.2

The Ultra Slim provides the highest charge percentage per dollar

Almost all of the Ultra Slim’s dimensions are the smallest among the battery cases we tested. At 152 millimeters tall, it’s only 2 mm taller than the shortest case, while it’s the narrowest at 70 mm, thinnest at 13 mm, and lightest, adding only 84 grams to the weight of the iPhone 6. Like a Model T, it’s available in any color you’d like, as long as that color is black. Anker uses the same kind of fingerprint-attracting matte plastic finish as many of its competitors.

The majority of iPhone battery cases can be divided into two categories when it comes to installation: sliders and front-frame-based cases. Anker’s Ultra Slim falls into the former camp. It has a short plastic cap at the top; you remove this cap to slide the iPhone in place, and then reinstall the cap. This is very easy to do compared to the trickier front-face design (used by Incipio, Odoyo, and some others), which require you to remove a frame that runs around the entire iPhone, install the phone in the base, and then snap the frame back into place.

Anker’s Ultra Slim Extended Battery case.

A micro USB port on the bottom of the case allows for charging the case’s battery (and syncing your phone), and the back hosts a power button and four battery-indicator lights. A 0.5-mm lip around the front edge protects the iPhone’s screen when you place the phone face down. Audio to and from the phone’s bottom microphone and speaker is routed through channels on the “chin” of the case (the area that extends beneath the phone’s Lightning-connector port and houses the battery’s circuitry).

Thanks to the iPhone 6’s larger size compared to the iPhone 5s, battery-case makers are able to squeeze larger battery cells into their cases. The Ultra Slim houses a 2850-mAh battery, compared to the 2300-mAh battery of our iPhone 5/5s pick, Lenmar’s Meridian. While the Ultra Slim’s capacity is definitely lower than that of the highest-capacity iPhone 6 battery case we tested (Mophie’s Juice Pack Plus has a 3300-mAh battery … and a $120 price tag), it performed on a par with some of the larger-capacity packs.

The Ultra Slim’s 120 percent of additional charge to an iPhone 6 isn’t the absolute highest of the models we tested but is still quite good, and it’s outstanding for the price.

Indeed, in our experience and testing, a battery’s stated capacity isn’t always a perfect indicator of actual performance. Depending on the efficiency of the charging architecture, you’ll sometimes get different results from batteries with the same capacity, or higher results from lower-capacity cells than from ones with higher capacity. In our tests, the Ultra Slim Battery Case delivered 117 percent of a full charge to the iPhone 6 (a 100 percent initial charge, then 17 percent on the subsequent charging cycle) in an average time of 2 hours.

Anker includes both a micro USB charging cable and a headphone-plug extender, which is pretty standard for battery cases. The latter accessory is necessary with many battery cases, because the iPhone’s headphone port is recessed into the case, making it difficult—if not impossible—to connect some headphones directly.

Who else likes it?

Jeremy Horwitz of 9to5Mac is one of the only other people we’ve found to have reviewed the Ultra Slim. “Unfancy but more polished than similarly budget-priced rivals such as uNu’s DX-6, it’s not the most powerful or beautiful iPhone 6 battery case I’ve tested, but it does precisely what most users want: it more than doubles the iPhone 6’s power, doesn’t add much bulk to the device, and costs very little relative to most battery cases.”

Amazon customer ratings are quite high for the Ultra Slim. With 654 reviews at the time of our most-recent update, the Ultra Slim’s ratings weighted average is 4.3 out of 5 stars. Other than a few minor complaints resulting in two- and three-star ratings, customers seem to like this battery case as much as we do.

Flaws but not dealbreakers

The Ultra Slim doesn’t have an especially premium feel. That’s not to say that it comes off as cheap, but there’s nothing about its physical construction that’s especially impressive compared to other cases. The matte finish easily attract fingerprints and grease, so compulsive iPhone owners may find themselves wiping it frequently. A lack of color options may also limit the appeal to some.

The Ultra Slim’s buttons aren’t covered, but the cutouts are properly sized and shaped.

Another minor strike against the Ultra Slim is a lack of button coverage. We almost always prefer (well-designed) press-through button covers that protect the iPhone’s various buttons and reduce the number of places where dust and dirt can get underneath the case. Here, we’re able to forgive the lack of button protection because the controls are recessed enough to keep them fairly safe from damage and accidental presses, and the holes are tailored tightly around the buttons. The downside is that it takes a more direct effort to use the controls, but it likely won’t be difficult unless you have exceptionally large fingers.

Buying Options

Anker’s Premium Extended Battery Case ($60) is the larger-capacity sibling of the Ultra Slim and a great alternative for those concerned more with raw power than size or cost—and even in those aspects, it’s a strong performer compared to the competition. With its 3,100-mAh cell, the Premium Extended is able to deliver a 142 percent charge to the iPhone 6. The only case to beat this performance is Mophie’s Juice Pack Plus, which costs twice as much.

The Premium Extended Battery Case is 71 mm wide, 152 mm tall, and 15 mm thick, and appears to either be based on the same reference design, or produced in the same factories, as a number of white-label models, including Trianium’s popular Atomic S. (We’ve reached out to Trianium multiple times to confirm whether the company’s case is MFi-certified, but we have yet to receive a reply. As such, we have not yet tested the company’s case.) Be that as it may, the case does exactly what it’s supposed to do, and it does it well. It provides enough juice to fill the iPhone 6 up once from empty, and then another 42 percent after the phone has been drained once more.

The Premium Extended Battery Case is close behind the Ultra Slim in charge percent per dollar, at 2.36 percent. It’s also a close runner-up in terms of cost per full charge ($42.79), and it’s the most efficient in terms of the percent of a full charge it provides per mAh. This one also wins in charging speed, delivering 1.11 percent of a full charge per minute. The rest of the battery cases clocked in right around 1 percent.

We don’t love that the Premium Extended Battery Case has a snap-on frame instead of a slider design, as the former is slightly more difficult to install on and remove from the iPhone. Thankfully, the frame includes button protection for the phone’s volume controls and Sleep/Wake button, and those covers are easy to find by touch and have a great, snappy click. The finish is very similar to that of the Ultra Slim, meaning it attracts fingerprints. Anker recently emailed customers about an issue that could cause the matte finish to come off the frame on some cases; the company will be sending out free replacements to all customers. (All new cases will ship with the updated frame.)

Long-term test notes

Some people who bought earlier versions of our runner-up choice may have noticed that the matte finish on the frame wears off too easily. Anker noticed too, and it has sent out an email to customers who’ve purchased the Premium Extended Battery Case saying that it’s fixed a production problem and will be sending out replacement frames to all customers, free of charge. If you'd like a replacement frame, contact Anker at 1-800-988-7973.

Buying Options

Prong’s PWR Case is an interesting alternative to standard battery cases. Its 2600-mAh battery isn’t the highest-capacity around, but two other features make this model stand out. The first is its two-piece design: Your iPhone fits into a fully protective case, and that case then slides into a separate battery pack. This approach lets you use the phone in the smaller case when you don’t need the battery, attaching the battery only when needed. (And it’s actually a pretty good case, considering that it’s not a standalone product.) The second unique feature is the case’s built-in charging mechanism. Fold-out wall-outlet prongs on the back of the battery pack let you to charge the phone and case anywhere there’s a wall outlet—without the need for a separate cable or adapter. These are really great features.

In our tests, the PWR Case provided 99 percent of a full charge to the iPhone 6s (we didn’t test it with the iPhone 6)—it doubles the phone’s battery life before you even have to think about using the prongs to plug into an outlet. The downside to the PWR Case is that it’s larger with the battery attached than the other battery cases we’ve tested. It’s best for anyone who values slimness but occasionally needs extra power when on the go.

Buying Options

The Smart Battery Case is Apple’s first foray into battery cases, coming almost eight and a half years after the company introduced the original iPhone. The design and material are essentially the same as those of Apple’s Silicone Case, but with a slight bump, 2.4 inches wide by 4 inches tall, protruding from the back. Unlike most battery cases, it uses a one-piece design: To insert your iPhone, you bend back the top segment and slide the handset down. Also unlike most battery cases, Apple’s offering has no on/off button: Your iPhone uses the battery case’s battery first, then the phone’s own battery.

Apple doesn’t advertise the Smart Battery Case’s capacity, instead citing performance metrics such as “increased talk time up to 25 hours, Internet use up to 18 hours on LTE, and even longer audio and video playback. Teardown site iFixit, however, has confirmed the battery to have a capacity of 1,877 mAh, which is much smaller than that our top picks (or most of the battery cases on the market). In our testing, the Smart Battery Case provided an average of 82% of a full charge to an iPhone 6s.

The design of the Smart Battery Case is unique, but Apple was also able to take advantage of the fact that the company makes both the phone and the software. For example, this is the only MFi-certified battery case with a Lightning-connector port for charging and syncing instead of Micro-USB—something we’ve heard many requests for. It’s also the only battery case that’s able to display the current charge level—of both the phone and the case—on the iPhone’s display, and you can see that information on both the lock screen and in Notification Center. Apple also says the case includes a “passive coupled antenna” that keeps the battery case from affecting cellular activity.

In person, the case looks better than it does in photos, and it feels pretty good in the hand, too. Most people with iPhone-battery concerns will be able to get through a busy day of use with the extra charge the Smart Battery Case provides, although we do wish the capacity was higher.3 You’re going to pay a premium for this one, but for some people, the unique features may be worth the cost.

Buying Options

Apple claims the 6 Plus should offer up to 24 hours of 3G talk time; 16 days (384 hours) of standby time; 12 hours of 3G, LTE, or Wi-Fi Internet use; 14 hours of video playback; or 80 hours of audio playback. In iLounge’s gaming test, the iPhone 6 Plus ran for 5 hours and 37 minutes. These are crazy long numbers compared to not only the iPhone 5s, but also the iPhone 6. Our hands-on experience confirms these results.

If you’re looking for the absolute most power for your 6 Plus, go with the PhoneSuit Elite 6 Pro. Its dimensions are pretty much identical to those of the Tylt model, but it has no slide-out shell; the extra room this design offers is used to house the single largest battery we’ve ever tested in a case, a massive 4200 mAh. The PhoneSuit has enough juice to fully recharge the iPhone 6 Plus, an impressive feat that no other case is able to manage. We think most people will get along fine with the Tylt, considering just how big the handset’s own battery already is, but the PhoneSuit is a great pick for raw power.

The Ultra Slim and the Energi Slider Power Case.

While all of these models feel particularly huge in the hand, the Energi Sliding Power Case hits the most right notes. While falling right between the others in terms of width and thickness, it’s the shortest we tested. And though it’s the heaviest at 151 grams—compared to 111 grams for the Mophie and 134 for the Boostcase—this metric is less of an issue than it could be, because you can remove the battery when you aren’t using it and go lighter. Just as with the iPhone 6 version of the Energi Sliding Power Case, the inner section of the case slides out. We especially appreciate this feature with the iPhone 6 Plus, which is already pretty big on its own. It’s great to have a protective case that can easily fit in most pockets, along with a separate battery sled that you can carry in your bag and use when needed.

There’s not much competition, but Tylt’s Energi Sliding Power Case is the best value when it comes to options for the iPhone 6 Plus.

When it comes to charging, we were very pleased by the results we got with the Energi Sliding Power Case. In an average time of one hour 23 minutes, the case delivered 83 percent of a full charge to a depleted iPhone 6 Plus in Airplane Mode. This is the fastest charge we saw, at 1.0 percent of a full charge per minute (compared to 0.61 percent for Boostcase and 0.65 percent for Mophie). The Energi’s charge rate per dollar comes out to 0.83 percent, and the cost for a full charge is $120.59, numbers that compare favorably to those of the Boostcase (0.70 percent, $143.72) and Mophie (0.73 percent, $136.37).

The competition

Spyder’s PowerShadow is somewhat notable for its optional charging dock. In our testing, the battery case’s performance wasn’t anything out of the ordinary. It’s also more expensive than our picks (especially if you include the price of the dock), and the dock’s chunky design isn’t particularly appealing.

Our previous favorite battery case for the iPhone 6 was uNu’s $70 DX-6. It’s still a strong contender, and it would likely have held onto the top spot if Anker’s cases weren’t in the picture. The 3,000-mAh DX-6 delivers a 126 percent charge, but with a charge percent per dollar rate of 1.8, it works out to $55.91 for a full charge.

In a previous edition of this guide, Incipio’s offGRID Express was the runner-up, coming in just behind the uNu DX-6. The offGRID Express delivers a pretty impressive 125 percent charge, but at its full retail price of $80, its numbers ($64.20 for a full charge, or 1.56 percent per dollar) fall in between those of the uNu DX-6 and the uNu DX-Free (below) in terms of value. That said, at the time of publication, it’s available for about $50 on Amazon, and it has been for some time. That lower price would make it a contender for the runner-up position, but Incipio has told us that this low price price is from a third-party seller, and there’s no guarantee it will last. If you’re able to grab the offGRID Express at that price, it’s still a good buy.

Incipio’s offGRID Shine ($90) houses the same 3,000-mAh battery as the offGRID Express, but instead of the Express’s two-piece, frame-style design (which we’re not terribly fond of), the Shine is a single piece. The Shine’s rubber border makes installation easier, because you simply slide the phone into place, and the back of the case is textured to look and feel like brushed metal. Two metal contacts on the bottom allow you to charge the case in an optional offGRID Dock, though you can still use the included Micro-USB cable if you’d rather not shell out for the Dock.

Unfortunately, serious problems with the actual charging process overshadow all these features. We tested three separate offGRID Shine cases, using two different iPhone 6 units; we experienced issues with every combination of case and phone. The most common problem was a rapid toggling, on and off, of the case’s power output with no provocation. Sitting on a desk, the iPhone’s screen would sometimes turn on and off as the phone indicated that its battery was beginning to charge, and then lose power, then sense power, and so on. Other times, this behavior happened only if the encased phone was lightly bumped–for example, if we gently set the phone down on a table. Sometimes, the case simply wouldn’t charge the phone at all.

Incipio tested one of the cases we had issues with, but reported that it worked find for them. Sites such as iLounge, 9to5Mac, and The Verge haven't reported the same issues, and have, in fact, been pretty positive in their reviews. So what’s the issue here? We really can’t say; we can only tell you that we saw it with all three units, and we haven’t seen similar behavior with any other case. However, it’s worth noting that even if it the offGRID Shine’s did work properly, its price would likely keep it out of contention for our top recommendation, given the strong performance and relatively lower price of the other options out there.

A new model from uNu, the DX-Free ($60), comes in right behind the DX-6. It has a much smaller (2,400 mAh) battery, and its performance drops significantly along with its capacity: The case delivered a 95 percent average charge in our tests. Though it weighs a few grams less than the DX-6, the other dimensions are pretty much the same, and it uses a snap-on frame design that we’re not huge fans of. In addition, in the second test we ran, the battery stopped charging at 64 percent; pressing the power button got it going again, at which point it delivered another 30 percent or so.

We wanted to like iBattz’s $90 Mojo Refuel Invictus Slim Battery Case, but it just didn’t live up to expectations. The big selling point with this one is swappable 3,200-mAh batteries. Ones comes with the case while extras can be purchased for $25 each. We’ve seen the concept work well with past products from the company, but with this one, the charge performance was middling, installation was difficult, and passthrough charging was wonky. When using the passthrough feature, the power supplied to the phone flickered on and off while it was connected, and the iPhone didn’t show up in iTunes as a connected device.

Odoyo’s Power Shell EX ($100) is one of the larger cases we tested, but it was in the lower half when comparing value numbers. The 3,000-mAh cell delivered a 116 percent charge to the iPhone 6, which is low for that capacity. One unique feature, however, is an integrated kickstand.

PowerSkin’s Spare ($80) is the least impressive case of the 19 we tested. It has the smallest battery (2,200 mAh) and, not surprisingly, provided the lowest charge (89 percent of a full charge). It was also towards the bottom in terms of value. On top of all that, the case itself offers less protection than any other, with open edges along the top and sides.

We tested two cases from Mophie, one of the biggest brand names in the category. (It’s not uncommon to hear someone refer to any battery case as “a Mophie,” much like someone might call a tissue “Kleenex.”) The company took a somewhat confusing approach to naming its iPhone 6 lineup: The Juice Pack Air ($100) and the Juice Pack Plus ($120) are for iPhone 6, while the aforementioned Juice Pack is for the iPhone 6 Plus.

As its name implies, the Juice Pack Plus is the larger of the two. It has a 3,300-mAh cell–the largest of any we tested for the iPhone 6–that gives you 149 percent of a full charge. That’s essentially the same charge-per-mAh efficiency as you’ll get with Anker’s Premium Extended Battery Case, but the Mophie costs twice as much. The general fit and finish of the Juice Pack Plus is very high, and we do appreciate having a dedicated on/off switch, which is less confusing than using a single button for power and battery level.

The Juice Pack Air is also a poor value. It provided the same amount of charge as the $40 Anker Ultra Slim, though in an arguably nicer, but larger, package. With both Mophie cases, you’re getting something that’s better designed than our top picks, but that provide less performance for the dollar.

Lifeproof’s Frē Power ($130) is unique among the cases we tested. Not only does it charge the phone, but like the rest of the company’s lineup, it protects the handset from the elements. Lifeproof promises the case can survive being submerged in two meters of water for an hour, as well as standing up to drops of two meters. All these features require sacrifices. The Frē Power is actually the least efficient case we tested in terms of charge percent per dollar, providing an average charge or 96% from its 2600-mAh battery. It’s also the single most expensive case we tested. But it stood up to a water test in a kitchen sink, and is respectably svelte for all that it offers. If you absolutely need both power and waterproofing, this one gets the job done.

PhoneSuit’s Elite 6 Pro ($100) is a nice looking slider-style case with button protection built in. The 3000-mAh battery exhibits pretty middling performance. The charge percent per mAh figure is right in the center of the pack, and with the high retail cost, its 121% average charge is towards the low end. Some users might also be confused by the capacitive touch panel on the back, which requires pressing one finger for some actions and two for others.

Boostcase’s Boostcase ($100) is similar to Tylt’s cases in that it uses a slide-out inner case with a separate battery pack. However, the Boostcase has a smaller battery for the same price, and its performance suffers because of it. The inner case is also less protective, as it’s a shell, rather than a full-protection case with button coverage. A clear version of the case provides identical battery performance as the black model we originally tested, but looks incredibly cool. It’s really quite neat to be able to see the electronic components, as well as the battery itself, inside the case.

Some of the least impressive performance for the price comes from Lenmar’s Maven ($100), which is somewhat surprising considering how much we like the company’s Meridian for the iPhone 5/5s. The Maven’s dimensions are identical to those of the DX-6. (We measured it at a gram heavier, but we’re willing to call that equal.) However, in our tests, the 3000-mAh battery 120 percent charge in 2 hours and 11 minutes, placing it at the bottom of the list for both cost per charge and charge percent per dollar and making it the most expensive per full charge. They’re small differences, but Lenmar seems to have mispriced this one. We wouldn’t be surprised to see the company reduce the price of the Maven in the near future; if so, it might move up in our list.

OtterBox’s Resurgence ($100) has one of the lowest capacity of the cases we’ve tested so far, at 2600 mAh. Not surprisingly, this resulted in relatively low charge numbers, averaging 103 of a full charge. You get more than just power with this model, though, as it’s the toughest case we tested: It’s the only case to claim MIL STD 810G-516.6 military drop protection, meaning it survived (in the company’s laboratory testing) drops of 48 inches on each face, corner, and back—a total of 26 drops. (As you might expect, this added protection means the Resurgence is also the one of largest overall of the battery cases we tested: It’s the tallest, and just a millimeter shy of the thickest and widest.) We appreciate the Resurgence’s button coverage, even though the sleep/wake button requires a little bit more pressure than it normally would. Protection for the ring/silent switch and for the case’s micro USB port is an added bonus. All things considered, the Resurgence isn’t a bad deal if you need the extra protection, but for most people, a less-expensive pick—with more battery capacity—will be a better option.

With a 2800-mAh battery, BuQu Tech’s PowerArmour ($80) has a slightly larger cell. The case brought the iPhone 6’s battery to just over a full charge (102 percent). What’s notable about the PowerArmour is its design. Instead of separating into two pieces for installation, it fits—and installs—like a standard iPhone case. To allow this, the case’s Lightning-connector plug slides down (and, thus, out of the way) for installation and removal; once installed, you slide the plug up and into the phone’s Lightning-connector port. You have to compromise left- and right-edge protection for this convenience, however. The PowerArmour’s height and width are the same as those of the uNu DX-6, but the former is 2 mm thicker. One cool thing BuQu Tech does that we’d like to see from more companies is include a physical-toggle power switch on the back of the case. BuQu includes this in addition to a button to display battery life, providing a simple way to toggle charging without having to worry whether you held a button down for the right amount of time.

The PowerArmour’s Lightning connector.

Dyconn’s i6 3200mAh Power Case ($90) is unique in that it includes a wireless charging dock for the case. The performance of the battery is only so-so, though: It provides 1.41 percent of a full charge per dollar, which is half that of the Anker Ultra Slim. The dock works well, and the package’s price is pretty good considering that you’d pay $30 or $40 for a similar combination from other companies (if it’s even available), but it’s not essential.

ZeroLemon’s ZeroShock Battery Case ($51) is definitely the craziest looking battery case we tested. The widest and tallest, it has big, extended corners that likely help protect against drops better than many of our picks, but also make the case less comfortable in the pocket. And the ZeroShock actually performed well, coming in right behind the Anker Ultra Slim in terms of charge percent per dollar. If you like the look, it’s not a bad purchase. We suspect, however, that it’s just too unappealing to recommend for most people.

The Atomic S from Trianium ($50) is physically identical to Anker’s Premium Extended Battery Case, including the same 3100-mAh battery. It fell short in our charging tests though, delivering an 18% lower charge than the Anker case. The price is also lower, but we suggest you stick with the Anker battery case as a high-capacity pick.

We’ve also tested some battery packs that aren’t proper cases in and of themselves, but rather, are meant to attach to the back of a bare or encased iPhone. There are a number of advantages to this style of power pack: They can be used with any Lightning-equipped iPhone, iPad, or even iPod; they can be easily removed when not in use, leaving your phone slim the rest of the time; and they generally cost less.

At $50, PowerSkin’s PoP’n 3 is a good buy in this category. The 4.4 by 2.4 by 0.5-inch battery sticks to the back of your iPhone or smooth case using suction cups and a micro-suction pad. It has a Lightning cable built in (a micro USB version is also available), so you just stick it on your phone and connect it when you need some juice. The PoP’n 3 hosts a 4000-mAh battery that in our tests delivered 158 percent of a full charge to an iPhone 6, doing so in 2 hours and 43 minutes: an impressive $31.65 per full charge, or 3.2 percent charge per dollar. The disadvantage, of course, is that it’s a separate piece to carry around, so if you’re actually looking for a battery case, well, this isn’t one.

Stacked’s Stack Pack for iPhone 6/6s (also available for iPhone 6 Plus and 6s Plus) is the latest case to offer wireless charging via a magnetic battery pack that attaches to back of the case. The package includes a protective case, a 2,750-mAh battery, and a magnetic charging base that plugs directly into the wall. Much like with the Tylt cases, the idea is to have a slim case when you don’t need additional battery, with the option to add power when it’s necessary. The Stack Pack’s case alone, however, isn’t much smaller than the Anker Ultra Slim battery case: 2mm thinner and about two-thirds the weight, but 2mm taller. Attaching the battery to the back of the case adds a pocket-unfriendly bump and more than doubles the weight. The Stack Pack is also not a new concept, as we saw similar models as far back as the beginning of 2014. If the price weren’t so high, we might see some value here, but at close to $100 more than our top pick, we can’t recommend the Stack Pack.

Footnotes

For the original version of this guide, we tested the batteries while the phones were connected to both AT&T’s LTE network and a local Wi-Fi network. However, this made it difficult to control for additional power draws such as notifications, the screen turning on due to notifications, a weak Wi-Fi or cellular signal, and so on. For this update, we opted to enable Airplane Mode for testing—including retesting all the models from the original batch—to ensure that the different batteries were each being tested identically.

Interestingly, despite the fact that the iPhone 6s’s battery has a lower capacity than that of the iPhone 6—1715 mAh versus 1810 mAh—we found that battery cases provide less charge to the 6s than to the 6. For example, the Anker Ultra Slim provides 117 percent of a full charge to an iPhone 6, but 108 percent of a full charge to an iPhone 6s. Though the difference differs depending on the battery case, there was a difference with every battery case we tested.

An iPhone 6s with the Smart Battery Case weighs almost the same as an iPhone 6s Plus in Apple’s Silicone Case. So if you’ve ever wanted the battery life of a 6s Plus with the size of the 6s, you can now get it (albeit with a bump on the back of the phone).